Magnetic Fields have a myriad of uses ranging from medical (MRI), chemical (NMR), motors, generators, high energy plasma physics, fusion reactors, particle accelerators, photon sources from synchrotron radiation, as well as many others. Although the creation of Magnetic Fields is a key aspect of various technologies, there are only a handful of known methods for creating Magnetic Fields.
Permanent magnets are one source of a Magnetic Field. They are naturally magnetic, but relative to other sources of magnetism, they are bulky and produce a weak Magnetic Field. Rare-earth magnets generally produce a stronger Magnetic Field compared to common iron-based magnets, but are too weak for most high-field uses.
Electromagnets create a Magnetic Field from an electrical current. Since the Magnetic Field is directly related to the electrical current, the strength of the Magnetic Field may be altered by increasing or decreasing the electrical current. Wrapping a current carrying wire into the form of a coil allows the Magnetic Field to be focused, increasing flux gain of the Magnetic Field. For larger Magnetic Fields, a superconducting wire is used to sustain a tremendous amount of electrical current while limiting ohmic losses (dissipated energy due to wire resistance).
Superconductors are currently the only viable option for generating large and persistent Magnetic Fields, for example those used in NMR. Unfortunately, superconducting magnets must be continuously cooled at temperatures at least below about 100 K (and typically around 4K), and the cryogenic systems needed to maintain these temperatures are cumbersome and expensive to operate.
In NMR, the Magnetic Fields are preferably strong, homogeneous, and stable. Although magnets, electromagnets, and superconductors are able to produce Magnetic Fields, the fields are difficult to make homogeneous and stable since even very minor material defects or winding defects in magnetic coils can cause significant field distortions. These imperfections are difficult and sometimes impossible to correct. Furthermore, in superconductors these imperfections cannot be easily determined until the magnetic coils are cryogenically cooled and in operation. The result is a Magnetic Field, which cannot be easily perfected and is inhomogeneous, thereby limiting NMR resolution.
Devices for generating small magnetic fields using direct current coils operating at room temperature have been developed to correct small distortions in the magnetic fields generated by superconducting magnets, and have become essential for improving NMR resolution. The magnitudes of these correction fields are typically 10,000 times smaller than the magnetic field produced by the superconducting magnet.
Therefore, it is desirable to have a device capable of generating a large Magnetic Field without requiring superconductors and the associated large cryogenic coolers. Furthermore, it is desirable to have a device capable of generating a large Magnetic Field that can be finely adjusted to create a strong, stable, and homogenous Magnetic Field.